Cylinder block assembly for a hydraulic device

ABSTRACT

A cylinder block assembly for a hydraulic device. The cylinder block assembly includes a cylinder block with a plurality of piston bores disposed therethrough. Circumferential grooves are disposed around the piston bore such that an elastic bushing may be disposed within the piston bore using a slip fit so that when the elastic material deforms the material deforms into the circumferential groove. By deforming into the circumferential groove the elastic bushing is locked in place and axial movement of the bushing in the bore is prevented.

BACKGROUND OF THE INVENTION

This invention relates to a hydraulic assembly. More specifically, thisinvention relates to a cylinder block assembly for an axial pistonhydraulic device.

In certain hydraulic axial piston pumps, a brass (or other material)bushing is inserted into the piston bore of a cylinder block. This isfrequently done because the bushing material has tribiological or otherproperties that are superior to those of the cylinder block material.

The current method for retaining bushings in the piston bores of thecylinder block relies on forces resulting from interference and frictionbetween the bushing and the bore into which the bushing is pressed toresist forces that would dislodge the bushing during operation. Anexpensive process that closely controls the surface textures anddiameters of two parts is currently used to ensure the bushing remainsin place during operation in the piston bore. Thus, a need in the artexists for a cylinder piston block that is both inexpensive, easy tocontrol and facilitates the manufacturing process.

Thus, a principal object of the present invention is to provide acylinder block assembly that is inexpensive to manufacture.

Another object of the present invention is to provide a cylinder blockassembly that facilitates manufacturing without compromising performanceor strength of the device.

These and other objects, features, and advantages will become apparentfrom the specification and claims.

BRIEF SUMMARY OF THE INVENTION

A cylinder block assembly for a hydraulic device. The cylinder blockassembly includes a cylinder block that has at least one piston boredisposed therethrough. A circumferential groove is disposed around thepiston bore such that an elastic bushing can be disposed within thebore. When disposed within the bore the elastic bushing deforms into thecircumferential groove to prevent axial movement of the bushing withinthe bore.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a cylinder block assembly;

FIG. 2 is a sectional view of a cylinder block assembly including abushing; and

FIG. 3 is a sectional view of a cylinder block assembly with a deformedbushing therein.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The figures show a cylinder block assembly 10 for a hydraulic devicesuch as an axial piston pump that utilizes an input shaft 12 to rotate acylinder block 14 as is conventional in the art. The cylinder block 14has a plurality of piston bores 16 disposed therethrough for receivingan axial piston (not shown).

A plurality of circumferential grooves 18 are disposed around each ofthe piston bores 16 on the inside diameter 17 of the bore 16. In apreferred embodiment the circumferential grooves are between 10 micronsto 4000 microns in depth. Elastic bushings 20 are disposed within eachof the piston bores 16 such that the outer diameter 21 of the elasticbushing 20 is disposed within the circumferential grooves 18 to preventaxial movement of the bushing 20 while in the piston bore 16.Specifically, the elastic bushing 20 once inserted into the bore 16expands and deforms into the circumferential grooves 18 to provide fullcircumferential contact with the cylinder block 14 within the groove 18so that the bushing 20 is locked and secured within the cylinder block14 as shown in FIG. 3.

In operation, the bushing 20 is inserted into the piston bore 16 with aslip fit and plastically deforms thus expanding the outer diameter 21 ofthe bushing 20. This creates pressure between the outside diameter 21 ofthe bushing 20 and the inside diameter 17 of the bore 16. Thus, thecircumferential grooves 18 allow the plastically deformed material ofthe bushing 20 to flow into the area created by the grooves 18. Thislocks the bushing 20 into place preventing the bushing 20 from beingremoved unless there is enough pull out force that causes shearing ofthe plastically deformed sections of the bushing. Thus, axial movementis prevented and the bushing 20 is secured within the cylinder block 14.

Thus provided is an improved cylinder block assembly 10 that requiresonly a slip fit between the outside diameter 21 of the bushing 20 andthe inside diameter 17 of the bore 16 prior to the expansion operation.Tight tolerances on the two pieces to be joined is therefore notrequired thus lowering manufacturing and assembly costs.

In addition, specific surface textures conductive to high frictionbetween the components do not need to be created using this new methodas compared to prior art manufacturing methods. This eliminates certainmanufacturing steps and lowers the cost of the assembly.

Additionally eliminated from the manufacturing process is the creationof a spiral groove on the outside diameter 21 of the bushing 20 torelieve hydraulic pressure or drain away fluid between the bushing 20and cylinder block 14. Thus, this eliminates a machining step for thebushing 20 and again, lowers the cost of the assembly 10.

Another step that is eliminated from the manufacturing process due tothe present cylinder block assembly 10 design is that the hydraulicpress that is designed to overcome forces from assembling parts when aninterference fit is presented is not required as in prior art methods.This eliminates a machine from the manufacturing process again,eliminating costs.

A final advantage provided is that there is no need to monitor andrecord the pressing force generated from overcoming the interference fitwhen inserting the bushing into the cylinder block bore. Again, costsare reduced yet performance and quality of the cylinder block assembly10 is not compromised. Thus, at the very least all of the statedobjectives have been met.

It will be appreciated by those skilled in the art that other variousmodifications could be made to the device without departing from thespirit and scope of this invention. All such modifications and changesfall within the scope of the claims and are intended to be coveredthereby.

1. A cylinder block assembly for a hydraulic device comprising: acylinder block having at least one piston bore disposed therethrough; atleast one circumferential groove disposed around the piston bore; and anelastic bushing disposed in the piston bore and within thecircumferential groove to prevent axial movement of the bushing in thebore.
 2. The cylinder block assembly of claim 1 wherein the elasticbushing is brass.
 3. The cylinder block assembly of claim 1 wherein thecircumferential grooves are greater than 10 microns in depth.
 4. Thecylinder block assembly of claim 1 wherein the circumferential groovesare less than 4000 microns in depth.
 5. The cylinder block assembly ofclaim 1 wherein the elastic bushing has full circumferential contactwith the cylinder block within the groove.
 6. The cylinder blockassembly of claim 1 wherein the elastic bushing deforms into thecircumferential groove.
 7. The cylinder block assembly of claim 1wherein the bushing within the circumferential groove secures thebushing in the cylinder block.
 8. The cylinder block assembly of claim 1wherein the hydraulic device is an axial piston pump.
 9. The cylinderblock assembly of claim 1 wherein the elastic bushing is slip fit intothe piston bore.